Single-chain nanoparticles (SCNPs) are well-defined nanoscale objects formed through the intramolecular cross-linking of individual polymer chains. A longstanding challenge in this field is the inability to synthesize SCNPs at high concentrations, an essential requirement for scalable production and practical applications. Here, we introduce an entropy-driven strategy that enables one-pot preparation of both noncovalently and covalently cross-linked SCNPs at concentrations approaching the polyme